The invention relates to a supply coupling of a fluorescent lamp comprising a supply transformer, a resonance circuit comprising the secondary coil of the transformer and a capacitor connected in parallel with the secondary coil, and a fluorescent tube connected in parallel with the resonance circuit and comprising fluorescent cathodes. The coupling is called a lamp circuit and used for igniting and burning a fluorescent lamp. Implemented according to the present invention, the coupling is also used for supervising the condition and operation of the lamp circuit. The coupling relates particularly to a supply coupling in connection with an electronic coupling device wherein the power required by the lamp circuit is supplied to the coupling by a transformer. The main use is in coupling devices which operate at voltages below a line voltage of 230 V.
Fluorescent lamps are generally used owing to their good lighting power. In addition, the long operating life of fluorescent lamps and the various tones of colour available enable their use in various applications.
Burning fluorescent lamps requires a supply coupling to supply the required ignition voltage to a lamp circuit and the supply voltage required during use. The problem with the current, known supply couplings in connection with lamp circuits is that when a fluorescent lamp or a lamp circuit is damaged, it is impossible to automatically switch off a supply transformer but the supply transformer continues to supply power to the lamp circuit until it is switched off manually. When the coupling is in operation again, the supply transformer has to be switched on again manually.
An object of the invention is to provide a supply coupling for fluorescent lamps to avoid the aforementioned drawbacks and to enable a lamp circuit to operate properly and the condition of the lamp circuit to be controlled such that the supply coupling can be switched on or off automatically independently of the working condition of the lamp circuit. This object is achieved by a supply coupling of the invention, which is characterized in that the coupling further comprises a direct-current supply arranged to supply direct current through a circuit comprising a first fluorescent cathode of the fluorescent tube, a secondary coil of the supply transformer, a second fluorescent cathode of the fluorescent tube and an indicator circuit arranged to detect the presence of said direct current and to generate a signal indicating that presence to be used for controlling a coupling device of the fluorescent lamp.
The invention is based on the idea that by supplying a low direct current to the supply coupling by the direct-current supply, the direct current being run through the galvanically-coupled components of the coupling, the intactness and operation of the components of the coupling can be controlled by measuring the presence of the current run through the coupling by the indicator circuit connected to the coupling. When the coupling is in working order in an ordinary operating situation, the direct current running through the coupling and measured by the indicator circuit is according to a predetermined value supplied to the coupling by the direct-current supply. If the coupling is damaged, in which case its resistance increases and the current decreases correspondingly, or stops running, the signal indicating the presence of direct current and being generated by the indicator circuit connected to the coupling can be used to generate a control signal, which is preferably a current or voltage signal. The coupling device, then, controlled by the control signal, automatically switches off the power supply from the supply transformer to the lamp circuit.
Similarly, after a damaged coupling starts working again after being fixed and the direct current supplied by the direct-current supply to the coupling starts running through the coupling again, the signal indicating the presence of direct current and being generated by the indicator circuit can be used to generate a control signal, which is preferably a current or voltage signal. The coupling device, then, controlled by the control signal, automatically switches on the power supply from the supply transformer to the lamp circuit.
The coupling device of the invention provides considerable advantages as far as controlling the condition, safety, usability and power consumption of supply couplings are concerned since a damaged lamp circuit is switched off and on again automatically depending on the condition of the supply coupling. In connection with changing lamps when, for example, a damaged fluorescent tube is replaced, the lamp will be switched on automatically with no need to re-introduce the lamp circuit into operation manually.